1) Field of the Invention
The present invention relates to an axial multi-piston compressor used in, for example, an air-conditioning system incorporated in a vehicle such as an automobile, and more particularly, to an axial multi-piston compressor with an internal lubricating arrangement for a shaft seal unit incorporated therein.
2) Description of the Related Art
Generally, an axial multi-piston compressor comprises: a cylinder block having a plurality of cylinder bores radially formed therein and arranged with respect to the central axis thereof; a plurality of pistons slidably received in the cylinder bores, respectively; a front housing securely fixed to an front end wall of the cylinder block to form a crank chamber therebetween; a drive shaft axially extended through the crank chamber such that the ends thereof are rotatabiy supported by the front housing and the cylinder block, respectively; a conversion mechanism provided on the drive shaft within the crank chamber for converting a rotational movement of the drive shaft into a reciprocation of the pistons; a rear housing securely fixed to a rear end wall of the cylinder block to form a suction chamber and a discharge chamber therebetween; and a valve plate assembly provided between the cylinder block and the rear housing.
The valve plate assembly in particular comprises: a disc-like member having sets of a suction port and a discharge port opened to the suction chamber and the discharge chamber, respectively, each set being able to communicate with the corresponding one of the cylinder bores of the cylinder block; an inner valve sheet attached to the inner side surface of the disc-like member and having suction reed valve elements formed integrally therein, each of which is arranged so as to open and close the corresponding suction port of the disc-like member; and an outer valve sheet attached to the outer side surface of the disc-like member and having discharge reed valve elements formed integrally therein, each of which is arranged so as to open and close the corresponding discharge port of the disc-like member.
When the axial multi-piston compressor is incorporated in an air-conditioning system for a vehicle such as an automobile, the drive shaft is rotationally driven by the prime mover or engine of the automobile, and the suction chamber and the discharge chamber are in communication with an evaporator and a condenser of the air-conditioning system through an inlet port and an outlet port formed in the rear housing, to circulate a refrigerant in the air-conditioning system. The rotational movement of the drive shaft causes the pistons to be reciprocated in the cylinder bores due to the conversion mechanism provided on the drive shaft within the crank chamber. When each piston is reciprocated in the corresponding cylinder bore, and thus a suction stroke and a compression stroke are repeatedly executed therein, a suction stroke is executed in one of the aligned cylinder bores. During the suction stroke, the suction reed valve element is opened and the discharge reed valve element is closed, whereby the refrigerant is delivered from the suction chamber to the cylinder bore through the suction port. During the compression stroke, the suction reed valve element concerned is closed and the discharge reed valve element concerned is opened, whereby the delivered refrigerant is compressed and discharged from the cylinder bore into the discharge chamber, through the discharge reed valve element.
In the axial multi-piston compressor as mentioned above, the crank chamber is in communication with the suction chamber and the discharge chamber through a supply passage and an exhaust passage formed in the cylinder block and having each a suitable control valve incorporated therein, whereby the crank chamber is filled with the refrigerant including a lubricating oil mist. Thus, movable parts of the conversion mechanism are lubricated by the lubricating oil mist included in the refrigerant, whereby a seizure of the movable parts can be prevented.
Also, in the above-mentioned compressor, a front end of the drive shaft is projected outside from an opening formed in a neck portion of the front housing, so that the drive shaft is operatively connected to the prime mover of the vehicle for the rotation thereof. In this case, of course, the crank chamber must be sealed from the outside so that a leakage of the refrigerant through the neck portion of the front housing can be prevented. To this end, a shaft seal unit is provided on the front end of the drive shaft at the neck portion of the front housing, to thereby seal the crank chamber from the outside. The shaft seal unit may comprises a mechanical seal element, a rubber lip seal element or the like.
As is well known, the shaft seal unit should be sufficiently lubricated with a lubricating oil during operation of the compressor, before it can exhibit a proper and good function thereof. Conventionally, it has been proposed that the refrigerant including the lubricating oil mist is utilized for the lubrication of the shaft seal unit. In particular, the shaft seal unit is in communication with the crank chamber through an oil passage formed in an end wall of the front housing, whereby the refrigerant can be introduced from the crank chamber into the shaft seal unit. Nevertheless, the conventional proposal fails to sufficiently lubricate the shaft seal unit with the refrigerant, because, although the refrigerant including the lubricating oil mist merely reaches the shaft seal unit through the oil passage, a sufficient amount of lubricating oil in a liquid phase cannot be fed to the shaft seal unit.